1. Field of the Invention
The present invention relates to a transistor for an organic light emitting diode (OLED) display device and a method of fabricating the same.
2. Description of Related Art
Conventional OLED includes an organic light emitting layer disposed between two electrodes. When an electron and a hole are respectively injected into the organic light emitting layer from the two electrodes, the electron and the hole couples to form an exciton. The organic light emitting layer generates light when the energy level of the exciton changes from an excitation state to a ground state. The OLED display device can be categorized as an active matrix type and a passive matrix type. The active matrix type OLED display device drives each OLED pixel using a transistor formed in the pixel.
The transistor of the conventional OLED display device is often fabricated based on a polysilicon structure which produces superior electrical properties to amorphous silicon structure. However, the transistor formed of polysilicon has several drawbacks. For example, the transistor may have a complicated structure, which causes low yield of the transistor fabrication and extended manufacturing time.
Accordingly, an OLED display device using amorphous silicon has been proposed. In order to be employed in the OLED display device, the amorphous silicon transistor should improve its electrical performance. For instance, the poor electron mobility of amorphous silicon limits the increase of luminescence of OLED display. The size increase of the transistor controlling the current flowing to OLED pixel may solve this problem, but decreases the size of display area. Thus, there is a need for increasing the luminescence without reducing the display area.